WordPress turned nine this year. According to Matt Mullenweg, a lead developer for WordPress, the open-source content management system (CMS) has been downloaded 145 million times (video). And a survey by W3Techs, which surveys and reports on technology usage, states that WordPress now accounts for more than half of all websites using a CMS, and nearly 17% of all websites of any kind.

WordPress didn't achieve such penetration by being a barebones CMS; out of the box, it offers a bevy of features that makes it ideal for authors, vendors, media producers and more. The addition of Retina support in WordPress 3.5, coming December 5, demonstrates that the developers are determined to keep their software up-to-date and versatile.

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But every user has individual needs that WordPress can't necessarily anticipate. That's why an active community of supporters and developers has produced more than 20,000 plugins. From modifying the core behavior to adding additional tools for administrators or readers, a wide range of problems has been encountered and solved through the use of third-party plugins, which are easy to install from the WordPress dashboard.

Inevitably, plugins change -- developers move on to other projects and functionality evolves to make old plugins obsolete. Among those I reviewed three years ago, a few remain relevant and supported -- most notably, Akismet for dealing with spam, All In One SEO Pack for improving your search engine optimization, NextGen Gallery for photo management and display and WP Greet Box for engaging new visitors to your site.

My list of essential plugins now includes not just those four, but also the following ten. Whatever the purpose of your site, these plugins will ensure a rich and trouble-free experience for you and your users.

WordPress has blossomed from its original role as a blogging platform into a full-featured content management system, able to host a variety of content types. If you want to serve audio and video podcasts, your best bet is the Blubrry PowerPress podcasting plugin.

PowerPress' configuration features plenty of options, each clearly documented. You can create a single podcast for an entire site or on a per-category basis, allowing multiple podcasts per domain. PowerPress feeds are compatible with iTunes and can be submitted to Apple's podcast directory. And publishing an episode is as easy as adding a filename to the associated blog post -- if there is something wrong with your file, such as the sampling rate, PowerPress will tell you. The resulting podcast can be streamed (using one of several players, including HTML5), downloaded or embedded as the producer sees fit.

PowerPress is free; there is a premium service that adds a number of reporting features for $5/month or $50/year.

Best of all, PowerPress is developed by Blubrry, which offers free statistics about your media. Finally, you can know just how many listeners or viewers you have.

There are free WordPress add-ons -- such as Jetpack, which is also reviewed in this roundup -- that can help you create simple forms that feature text fields, checkboxes, radio buttons, etc. For a more powerful take on this functionality, try Gravity Forms, a commercial plugin.

Gravity Forms has all the basic form-building features and then some, including conditional fields, anti-spam CAPTCHAs and honeypots, and the ability to store data directly into WordPress's post database. With Gravity Forms, it's possible to create forms for event calendar submission, event registration or WordPress post entry -- the latter being especially useful if you're an editor who wants to protect your authors from the WordPress dashboard.

A license to use Gravity Forms on a single site is a reasonable $39/year; pricier tiers come with additional sites and functionality (such as PayPal and MailChimp integration). The plugin doesn't cease functioning at the end of the year, but updates and support become unavailable. Since security flaws or WordPress updates can break a plugin, it's risky to let a Gravity Forms license expire, so users are best off renewing.